Simple, Small-Sized Fuse

This invention relates to a small fuse which blows at the fixed temperature to break a circuit. More particularly, this invention provides a simple, small fuse comprising two lead wires supported in parallel by a heat-resisting, insulating support which is covered with a frame. A conductor bridges said lead wires with both ends fixed to each lead wire by an alloy having a low fusing point, and a heat-resisting elastic substance is urged to upward against said conductor so that upon fusing of said alloy of low fusing point the conductor is freed from connection with said lead wires and the insulating filler, such as insulating grease, in the frame.

The complete nature and full advantage of the present invention will be understood more clearly from the description made with reference to the attached drawings in which:

FIG. 1 is a longitudinal section of the fuse according to the present invention in its normal state.

FIG. 2 is a side elevation of the fuse shown in FIG. 1, cut vertically.

FIG. 3 is the fuse according to the present invention as operated.

FIG. 4 shows the fuse according to the present invention, in which a cap member is placed on a coiled spring.

In the drawing, a support 1 is made of highly insulative and heat resistive material. This support 1 is covered by a frame 5 made of insulative and heat-resistive material in such a fashion as to form a hermetically sealed chamber. Two lead wires 2, 2 are led, in parallel with each other, into the frame 5 with a fixed space therebetween and are fixed to the support 1. Said lead wires should be good conductors, such as copper or silver-plated wires, and are supported hermetically by the support 1 at the led-in portion or the other portion with a binder, such as epoxy resin. A conductor 3 is provided in such a fashion that it makes contact with the end portion of each lead wire within the frame 5, and contact points 4, 4 between the conductor and the two lead wires are fixed together by an alloy having a low fusing point comprising an eutectic compound. Insulative filler, such as grease, is filled into the frame. This insulative filler is intended to prevent oxidation of the alloy and to withstand the voltage between the two lead wires after fusing. Therefore, special grease 6 which is highly heat resistive and insulative is used as filler. In order to separate the conductor 3 from the lead wires sensitively, in other words, in order to make the fuse according to the present invention operate competently as soon as the alloy reaches its own fusing point, a heat resistive and elastic coiled spring 7 is inserted into a concave opening 8 in the support 1 and is compressed so that it is urged to upward against the conductor 3. In this connection, if the head of the coiled spring is covered with a cap member 9 of rivet-shape, it will make smooth the slipping of the coiled spring in and out of the concave 8.

According to the present invention, the fuse in its normal state is stable as shown by FIG. 1, and if the alloy of low fusing point fuses, the elasticity of the compressed coiled spring 7 instantly separates the conductor 3 from lead wires 4. At the same time, the circuit is broken, as shown by FIG. 3. This performance of the coiled spring, together with the insulating effect of the insulating grease filled in the frame, checks the occurrence of trouble due to re-connecting of the conductor with the lead wires.

The fuse according to the present invention is, therefore is simple in construction, sensitive in operation, and involves no fear of re-connecting after being blown. Thus, the fuse according to the present invention can be used safely.